Spiny Water Flea
(Bythotrephes longimanus (Leydig 1860)
2002 Invasive Species Symposium
Date: June 18-19, 2002
Location: Freeborn Hall, University of California-Davis - Davis, California
American Fisheries Society 132nd Annual Meeting: "Turning the Tide - Forging Partnerships to Enhance Fisheries"
Date: August 18-22, 2002
Location: Baltimore Civic Center - Baltimore, Maryland
Zooplankton make up the animal portion of the living, floating particles in aquatic systems. They are highly varied in size and morphology and as primary consumers, feed on bacteria, algae and other zooplankton. Zooplankton are in turn eaten by fish, mollusks, crustaceans, and even mammals, thereby providing an integral link between the food web foundation and its higher members. Branchiopods are a class of crustaceans that use their flattened feet covered with thousands of hair-like setae to filter food out of the water. A specific order of branchiopods are the cladocerans, commonly known as the water fleas because of their swimming motion. Cladocerans brood their young in their carapace and all but two species contain a single compound eye. Apart from their detailed anatomy, cladocerans are distantly related to crabs, shrimp, and lobsters and are almost entirely freshwater species. Cladocerans have a wide array of different morphological features. Their variability is illustrated in Southwest Missouri State's zooplankton photo gallery. Daphnia species are probably the most well known genus of cladocerans but the order contains around 80 genera containing almost 400 species. A detailed taxonomy of the order can be found at the University of Guelph, Ontario's webpage.
The spiny water flea is a predatory cladoceran species, which feeds on other zooplankton (36) . Adult Bythotrephes (bith-o-TREH-feez) measure around 1cm (.4 inches) in length and are much larger than most zooplankton species native to the Great Lakes. They are characterized by a long caudal tail spine that is barbed and makes up over half the animals body (1, 26) . Longer tail spines with a characteristic 'kink" are associated with the parthenogenically reproduced individuals once thought to be a distinct species, B. cederstroemi Schöedler (2, 46, 51) . For the purpose of clarity the genus name, Bythotrephes, is used to describe all the spiny water fleas. Morphological differences between these animals can be seen in Peder Yurista's paper available through SeaGrant's Nonindegenous Species (NIS) site. As they grow and molt they gain barbs on the tail spine. Their recent introduction into parts of Europe, Canada and the United States has caused alarm over the potential effects a new zooplankton predator is having on the food web assemblage.
Native Range & Biology: Bythotrephes is a native inhabitant of many European Lakes that vary in fish composition, size, depth, and water quality (38) , (32) . It ranges throughout the Palearctic from Great Britain to the Bering Sea, but successful invasions into more European lakes have made its original distribution ambiguous (17, 23) . The worldwide distribution of Bythotrephes, including its native and introduced ranges, is well mapped by the Group on Aquatic Alien Species (GAAS), a subprogram of the Regional Biological Invasions Center (RBIC).
Bythotrephes can reproduce both by parthenogenesis (cloning) and sexual reproduction. Morphological differences are characteristic for each type. Within the embryo, parthenogenic individuals develop through a red-eye into a black-eye stage before breaking out of the brood sac. Individuals reproduced sexually undergo a “resting egg” stage. Once born, both types develop through consecutive molts but retain their characteristic tail (kinked or not). During molting individuals gain “barbs” above their tail spine but the number also is variable. Fully developed parthenogenic individuals have three barbs gained through 2 molts, sexually reproduced individuals end up with four barbs through 3 molts and males have only two, not gaining a barb during their final molt (51) .
Through parthenogenesis the spiny water flea can exhibit explosive population growth, but its ability to produce sexual eggs allows it to increase genetic variability as well as survive and disperse under adverse environmental conditions (19) . Minnesota Sea Grant has an illustration of the alternating reproductive cycle of the spiny water flea. Development time till primaparity (1st time mom) is not significantly different for the two modes of reproduction, averaging about 14 days (51) . Sexually reproduced eggs can go into a semi-static metabolic condition called diapause. Through these sexual reproduced “resting eggs”, the next generation of Bythotrephes can overwinter and hatch usually when temperatures exceed 4ºC (52) . The spiny water flea can survive a wide range of temperatures, but has lowest mortality between 5ºC and 30ºC (16) . Its development time is temperature dependent and maximized between 20-25ºC without suffering higher mortality (51) . Besides protection from winter conditions, many diapaused eggs can also survive passage through fish digestive tract (21) . A female with a full clutch is double her usual weight (44) . This fact causes increased predation on pregnant females above their conspicuous body with a single large eye and long tail spine and thereby further aids in dispersal (21) .
Bythotrephes is an integral element of freshwater food webs in its native range feeding on phytoplankton and zooplankton as well as being a prey item for fish. Through predation it limits many zooplankton species that are herbivorous (20, 50) . Its larger size compared to other zooplankton and prominent eye make the spiny water flea a preferred prey for many fish (12, 29, 35, 37) . In some Russian lakes fish predation has eliminated it while in shallower lakes without fish, it can reach densities of 125 m-3 (47) . The lack of coadaptation of predators and prey in its introduced range make the spiny water flea’s impacts much more significant and damaging to the food web.
Introduced Range & Biology: Recent introductions of the spiny water flea into the Great Lakes region as well as European ports in Belgium and the Netherlands have prompted questions about the origin and mechanism of its invasion. Through genetic techniques, Bythotrephes introduction across most of the world have been tracked to a distinct donor region through the Port of St. Petersburg (2-4, 32) . The spiny water flea is a native inhabitant of Lake Lagoda in this region. Because of the strong fresh water input by the Neva River, the port is either freshwater or has very low salt content (oligohaline) at many times of the year. Inhabitants of Lake Lagoda are also the primary components of the zooplankton community of St. Petersburg harbor (45) . The ballast water taken up by transoceanic vessels is also freshwater and allowed Bythotrephes along with other recent invaders to traverse the saltwater barrier that lies between its native and introduced ranges (2, 4, 32, 39, 43) . Bythotrephes reproductive potential is one of the most important aspects of it biology allowing for this expansion. Successive invasions from further ballast water though have actually increased the genetic variability of the Great Lakes populations above that of simple sexual reproduction (4) . The initial release of the spiny water flea was probably a casual release from a shipping boat of a few million gallons of ballast water.
The spiny water flea first arrived into the Great Lakes region specifically Lake Ontario in 1982 (22) . By 1987, the spiny water flea was present in all the Great Lakes (8, 13, 22, 24, 25) . Subsequently it has spread into northern U.S. and Southern Canadian lakes totaling 66 North American lakes at the beginning of 2002 (46) . Besides J. Borbely’s (2001) diagram below, GAAS also has a good diagram on the North American range. Like many other marine invasions to these lakes it has arrived through the ballast tanks of ships (4, 10, 34, 43) . Fish predation within certain lakes has already begun the process of natural selection based on size of the individual invader. The selection process and differences between individuals have begun compounding to shift the size of certain populations. Within the Great Lakes, individuals are largest in Lake Michigan while smallest individuals are being selected for in Lake Erie and Huron (20, 44) .
Belgium and the Netherlands have also been under siege from the exotic spiny water flea first reported in the Biesbosch reservoirs in 1987 (48) . Bythotrephes has since expanded its introduced range in this area as well. It now occupies Lake Volkerak-Zoom and the Broechem Reservoir, Belgium and continues expanding (23) . Like the other introductions, human-mediated dispersal around its native territory has also expanded its current range in the Commonwealth of Independent States, formerly the U.S.S.R. (17) .
Known & Potential Impacts: The spiny water flea occupies a mid-level trophic position and therefore affects species that are both above and below it in the food chain (27) . Recent studies have attempted to single out interactions between the spiny water flea and either its prey, competitors or predators. Small crustaceans like Daphnia species are known as the main prey for Bythotrephes in its native range (36) . In the Great Lakes, the spiny water flea has caused major changes in the zooplankton community structure (9, 14, 20, 26-28, 41, 50) . It also has increased competition with small fish and native predatory zooplankton like Leptodora kindtii (16, 50, 53) . Fish species that formerly preyed upon Daphnia sp. and Bythotrephes’ competitors have been forced to shift their diets, many to the invader (6, 7, 12, 21, 35) . This exemplifies that the ripple effect Bythotrephes is having on Great Lakes food webs should be viewed from a variety of perspectives.
The spiny water flea had almost immediate effects on zooplankton assemblage upon its introduction into the Great Lakes collapsing some Daphnia populations (9, 28) . Two particular species, D. retrocurva and D. pulicaria, both collapsed in Lake Michigan while a third species of the pre-invasion community, D. galeata mendotae, also showed declines but rebounded and now solely dominates the Daphnia position in the zooplankton community (25, 26, 28, 41) . Declines in Daphnia species have been recognized in both large and small lakes (20, 28) . Overall, the spiny water flea consumes about 25% of zooplankton production. The effect on zooplankton is stronger during certain times. During its peak in late July and August of 1995, Bythotrephes consumption in Harp Lake, Ontario exceeded production (i.e. reproduction) of all zooplankton by 20% (14) . Moreover, this was just two years after its introduction there! In Lake Michigan it preys on the largest zooplankton individuals unlike normal crustacean predators (41) . These results though are at odds with results from the much smaller Long Lake (20) . Another zooplankton known as Holopedium gibberum also showed drastic declines in Lake Michigan after the spiny water flea’s introduction. Holopedium has a gelatinous sheath that is good protection from its normal predators like Chaoborus, however, it seems not to limit predation by Bythotrephes (33, 41) . Again these results are different from smaller lakes where H. gibberum actually showed significant increases in abundance (50) . Different effects on zooplankton depending on lake size may be a function of the prey availability and higher densities both of predator and prey. The spiny water flea is an opportunistic predator mainly feeding on Daphnia but diet switching when abundances become low (20) . In some instances then Bythotrephes’ invasion has collapsed the local populations, but its role in freeing other species from competition or predation has increased their abundance.
Many of these Bythotrephes zooplankton prey are the usual food of juvenile and small fish as well as other predator zooplankton like native Leptodora kindii. Lehman (1988, 1991, 1993) espoused that declines in the native Leptodora is due to increased competition for its usual prey like D. retrocurva and D. pulicaria. Bythotrephes also preys on Leptodora causing further declines in their populations. Increases in Bosmina, a normal prey species of Leptodora, are thought to be indirectly related to the spiny water flea’s competition (41) . Juvenile fish were major predators of Daphnia species prior to the invasion of Bythotrephes. Its new competition and effective limitation as a prey species for smaller fish due to its tail spine (1, 35) could be causing decreases in recruitment potential for fish (6) . Bythotrephes tail spine is most likely creating a selective pressure for larger mouth gape in juvenile fish so they can utilize the invader as a prey item. More research is needed to determine if this selective pressure is a realized event.
Bythotrephes unclear effect on fish recruitment aside, larger fish have shown strong diet switching and even preferred the invader as a food source. It has provided a strong source of prey for alewife, herrings, two perch species, shiners, walleye, chub and other fish throughout the Great Lakes (7, 18, 35) . Yellow perch nearly doubled their zooplankton predation after the invasion and selectively feed on the invader along with white perch and bass (7, 35) . More than 60% of alewife diets in spring of 1988 were Bythotrephes (35) . These smaller fish are also prey to larger game fish like salmon and lake trout. Deborah Swackhamer is conducting ongoing research on PCB concentrations in salmonids due to Bythotrephes introduction into the food web. Magnification of this potentially lethal chemical is caused by a buildup effect through Bythotrephes, its predator the alewife and larger prey like introduced salmon. By better understanding the individual changes in species diet and composition the spiny water fleas introduction has caused, we can gain a clear picture of the wave of effects small invaders can have on massive systems.
Management: As with many ballast-mediated invasion management begins with prevention. Bythotrephes is only one example of the massive amount of invasive species that continue to inundate the United States coastlines and estuaries every year. Shipping alone accounts for 51% of 298 Nonindigenous species (NIS) initial invasions into United States waters (40) . Combined with fisheries, this vector accounted for almost 90% of all initial marine invasions. The problem associated with ballast water marine invasions is outlined in detail by the Global Ballast Water Management Programme.
The accidental introduction of ballast water invaders like the spiny water flea, the zebra mussel, and others could possibly have been avoided by ships using open water ballast exchange practices. In the United States, the National Invasive Species Act of 1996 (NISA summarized by NEMWI) has directed the Coast Guard and the Smithsonian Environnmental Research Center to develop a Clearinghouse to gather and disseminate information on ballast-water invasions, regulations, and practices so legislation can be implemented to reduce marine invasions. However, current practices are limited in their control of ballast invaders with two recent invaders, Cercopagis pengoi(31) and Echinogammarus ischnus (49) arriving after implementation of current guidelines.
Total ballast water exchange is usually impossible due to the shape of tank leaving residual waters to mix with new seawater. Species that have resistant resting stages (like Bythotrephes) and come from euryhaline systems like the Ponto-Caspian one are more likely to survive this control effort (39) . Chemical control, most likely chlorine, is not really an option because it strongly affects lake trout along with upsetting many other ecosystem inhabitants. Successful legislation has been passed in Michigan and Canada to provide detection, regulations and economic incentives for ships that comply with invasive control procedures. New provisions by the Canadian government call for updating of shipping vessels as well as required open ocean exchange. Michigan legislation goes above the federal standard of recommended voluntary open ocean exchange.
Current management practices for the spiny water flea seek to limit its spread to other lakes. Predictions can be made on the invasion potential for surrounding areas using the vectors of transfer, namely humans. Using gravity models, a type of statistical analysis, one can map predictions of potential lakes in future invasions through the incidence of human activity and contact with Bythotrephes. Gravity modeling correctly predicted 11 lakes as having higher vectors from invasions sources from 2000 to 2001(5) . One main factor is the lakes proximity to major roads and lakes within 3.4 km show particular vulnerability. (5) .
Personal management practices for boaters and anglers include cleaning of boating equipment with high-pressure water or heated water upwards of 104ºF. Also bait buckets should not be emptied into waters, instead empty on land. Visual inspection of rigging, fishing, and anchor lines as well as the props and hulls of boats can help limit the spiny water fleas spread. Both types of invasive fleas look and feel like wet cotton on fishing lines. Boats should be allowed to dry for at least 5 days before transport between lakes, but because of Bythotrephes resting eggs longer periods are recommended. Boats and trailers can be towed through carwashes if exposed to infected waters for long time periods. Some antifouling paints can limit the attachment of aquatic pests like zebra mussels or the spiny water flea. Any waterweeds or plants should also be removed. These practices are outlined at the Sea Grant and GLERL waterflea site.
As invasions through ballast tanks are becoming more common, especially through this Ponto-Caspian corridor, invading species may have a higher chance of survival in the recipient area (39) . It has long been developed that diversity of community structure repels invaders through biotic resistance (11, 15, 30) . In Bythotrephes case, as is being realized for many aquatic systems, diverse species composition was not a successful repellant to invasion (12) . Multiple waves of invasion of coevolved species may also facilitate one another’s’ successful invasion thereby causing an accelerated rate of introduction called “invasional meltdown” (39, 42) . Only through control of this invasion corridor both economically and biologically, can the tide of invading aquatic species ebb.
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The Spiny Water Flea
Photo courtesy of Michigan Sea Grant
Shipping lanes provide a unique route of access for marine invasive species. The recent invasion of the Spiny Water Flea into the Great Lakes is a prototype for understanding how ballast tanks of ships can mediate invasions over large geographic distances.
Bythotrephes hitched a ride on a commercial shipping vessel and invaded Lake Ontario sometime in late 1982. Genetic comparison shows that Bythotrephes most likely came from the port of St. Petersburg, Russia. It rapidly spread, invading all of the Great Lakes by 1987. Belgium, the Netherlands, and parts of Germany have also been recently invaded. The spiny water flea has been reported in inland lakes of Ontario, Michigan and Minnesota. Its continued spread could have detrimental effects on food web stability in many freshwater lakes.
Upon its entry, the spiny water flea rapidly multiplied to become a major factor in the food web. Bythotrephes is a dominant predator of zooplankton during its peak from mid-July to early August. Although the ripple effect Bythotrephes has on food webs is only starting to be realized, changes in zooplankton abundance have caused diet shifts in other plankton predators like herring, alewife, and bloater chub. Many of these species are important prey for larger game fish like introduced salmon and lake trout.
This invading zooplankton may establish itself as a stable link in the dynamic food chain of the lakes. Bythotrephes has no doubt forced some members to shift their feeding habits but they may be able to feed on the new invader. The spiny water flea's introduction has already been instigated in the disappearance of 2 species of Daphnia, herbivorous cousins and prey of the invader.
In this picture, a female carries her egg sac on her back.
Photo Courtesy of J. Lindgren
Because of their ability to reproduce by sexual reproduction and parthenogenesis (genetic copies), the spiny water flea needs only a single successful female invader to colonize. An individual female Bythotrephes offspring at summer temperatures (12.7 °C) can develop to sexual maturity in around 14 days (Yurista 1992).
Diapausing eggs of Bythotrephes
Photo courtesy of Henk Ketelaars
Sexually reproduced eggs in Bythotrephes go into a state called diapause, a resting phase where they can resist large environmental changes. These diapausing eggs are able to survive during winter and even survive passage through fish digestive systems (Jarnagin et al. 2000) No doubt the resilience of this invaders diapaused eggs will continue to aid in its dispersal and survival.
- Kingdom: Animalia
- Phylum: Arthropoda
- Sub-phylum: Crustacea
- Class: Branchiopoda
- Order: Cladocera
- Suborder: Onychopoda
- Family: Cercopagidae
- Other names: Through recent genetic techniques the former two species of this genus have been resolved into one species. Its former name was B. cederstroemi, the form most commonly found in the U.S. (Therriault et al. 2002).
Photo courtesy of Jeff Gunderson
The spiny water flea attaches to fishing lines and anchor lines en masse in the height of winter. They are generally thought as only a nuisance to fisherman and boaters. By changing the food web, however, Bythotrephes may shift abundances of recreational and commercial fish species.
*Without magnification, most of these species will look similarly microscopic. Explore the identification aids below to understand how to notice these invaders on a human scale.*
Photo courtesy of Dr. Flinkman;
Finnish Institute of Marine Research
A new water flea, the fishhook flea (Cercopagis pengoi) invaded Lake Ontario in late 1998. It has spread throughout the Great Lakes. Like the spiny water flea, it collects in masses on fishing lines and boat ties and is also a Ponto-Caspian invader from ballast tanks.
Photo courtesy of the University of Guelph, Ontario
A native cladoceran, common to the Great Lakes, Daphnia mendotae has a helmet-shaped head which can help in identification. It commonly hybridizes with other introduced Daphnia species like D. galeata, a European introduced species resulting in a variety of morphological variations.
Photo courtesy of the University of Guelph, Ontario
Another introduced Daphnia species, D. lumholtzi is a cladoceran that is slowly making its way towards the Great Lakes via channels and river systems from the south. Many other cladocerans inhabit the Great Lakes and more are being introduced accidentally.
The Daphnia pages of the Cladoceran website can help in identification of this genus' many species.
This close up shows you how similar these different species can look even with magnification.
Female Bythotrephes with eggs
Photo courtesy of Henk Ketelaars
Identification of the spiny water flea by anglers can sometimes be confused with its recent fellow invader the fishhook flea (C. pengoi). Both collect on fishing lines and have characteristic tails. On a fishing line, both invaders look like cotton clumps along the line.
Bythotrephes clumped on a line.
Photo courtesy of University of Minnesota Sea Grant
Specific differences lie in the shape of the tail and the larger relative body size of the spiny water flea. Body differences are shown on the Waterflea Identification Guide.
Anglers and boaters can help prevent the spread of the spiny water flea and other aquatic invaders by following prevention methods outlined by Sea Grant and GLERL. Although many lakes are already invaded, the public can hinder the spread of these nuisance species. Early prevention and identification through the public is an important aspect of control.
Education is probably the most important restraint for aquatic pests. By informing others, you can inform fellow anglers and boaters on smart practices to keep fish populations and ecosystems more stable.
If you need more information about this species, please contact:
In the United States:
Make an online report at the GLERL/Sea Grant Waterflea Reporting Site.
Ontario Ministry of Natural Resources
Regional Office: Thunder Bay
435 S. James St.,
Suite 221 P7E 6S8
Report sightings by calling the Invading Species Hotline:
All available literature on the spiny water flea (Bythotrephes) is available online through the National Aquatic Nuisance Species Clearinghouse by selecting Bythotrephes under Crustaceans.
If all else fails, contact Todd Campbell of the Institute for Biological Invasions at firstname.lastname@example.org, who will forward your message to the appropriate person.
Please Cite this Page as:
Sikes, Benjamin A.. 2002. Spiny Water Flea, Bythotrephes longimanus. Institute for Biological Invasions Invader of the Month.
More Spiny Water Flea Online
- The spiny water flea, Bythotrephes cederstroemi: Another unwelcome newcomer to the Great Lakes
Provided by Ohio Sea Grant/ Dr. David J. Berg
- Life history and effects on the Great Lakes of the spiny-tailed Bythotrephes
Provided by Minnesota Sea Grant
- Spiny Water Flea in the Great Lakes Region
Provided by GLIN (Great Lakes Information Network)
- Bythotrephes waterfleas ongoing projects
Provided by Hugh MacIssac at the University of Windsor
- Zooplankton of the Great Lakes: Bythotrephes cederstroemi
Provided by Central Michigan University